The present invention generally relates to the formation of holes in a substrate material, typically an unfired, ceramic xe2x80x9cgreensheet,xe2x80x9d for the purpose of fabricating electronic circuit components which are ultimately used in the manufacture of electronic devices such as computers or the like.
Circuit boards with multiple VLSI circuit chips are called Multichip Modules (MCM). The use of VLSI circuits presents interface problems relating to the interconnection of the integrated circuits to other circuits and the placement of the integrated circuits on a ceramic circuit board (MCM-C). As VLSI technology has advanced, the density of circuits on a single VLSI chip has increased and the necessary interconnection for VLSI chips has become increasingly difficult to achieve in a limited space. An MCM-C design object is to increase the ratio of the total area occupied by silicon to the total board area, called silicon efficiency ratio. The MCM-C packaging limits the speed and size of a system. Because the physical interconnection is a limiting design factor, a way to accommodate more circuit interconnections is necessary.
In a typical configuration, semiconductor chips are mounted in cavities on multilayer circuit boards and the circuit boards accommodate intercircuit connections through tiny vertical holes or vias between the layers. The chips are connected to the vias using a controlled-collapsed-chip-connection technique called C-4. The vias are filled with a conductive material, such as molybdenum paste, which creates a connection to the VLSI circuit. The size of the holes dictates the size of the connection and the number of connections that can be placed on the multilayer circuit board.
There are a number of methods for creating small holes in precision tooling to facilitate the punching of vias. Such methods include dry or laser cutting and electrical discharge machining (EDM). The precision tooling of each of these methods facilitates the punching of vias as small as 0.01778 cm (0.007 in.) in dielectric material as thin as 0.00762 cm (0.003 in.). The precision tooling is used in a master punch and die assembly.
In the precision punching method, each precision via hole is punched in a workplace or substrate using precision tooling which includes a precision punch assembly and a precision die assembly. The punches of the precision tooling device are guided by precision holes in one or more precision plates. The cutting edge of the die plate is formed by precision openings in the die plate. The precision of the tooling is the limiting factor in providing a precision punch substrate. Prior art is directed to the precision necessary to create the smallest possible precision holes in a substrate.
The vias necessary to create the circuit interconnection have previously been created by a punch and die device which is fabricated by making a die mask or plate using EDM. The plate is fabricated from 0.127 cm (0.050 in.) tool steel. Precision holes as small as 0.1651 cm (0.0065 in.) are burned through two plates at one time by EDM at a rate of 6 holes per hour. The plates are then used in a precision tooling device. The size of the substrate hole punched by the precision tooling is limited by the size of the smallest plate opening which can be created by EDM, namely 0.01651 cm (0.0065 in.). The EDM plate facilitates punching holes with an accuracy of 0.00762 cm (0.003 in.) true position. These tool steel plates are heavy, expensive, and require sharpening. The sharpening consumes time and can only be done several times before the die must be replaced due to wear.
A method for producing precision dies is disclosed in co-pending U.S. patent application Ser. No. 08/660,611 filed Jun. 6, 1996 and titled xe2x80x9cPrecision Punch and Die and Construction.xe2x80x9d The copending application is incorporated herein by reference.
Numerous types of punching devices are found in the prior art. For example, U.S. Pat. No. 4,821,614 describes a punch apparatus with a single punch element and a programmable apparatus to selectively move a carriage which supports the sheet of material being punched. Another punch apparatus with a single element is described in U.S. Pat. No. 4,872,381. IBM Technical Disclosure Bulletin, Vol. 20, No. 4, September 1977, pages 1379-80, discusses a punch apparatus with a plurality of individually activated, programmable, punching elements. The substrate to be punched is supported by a movable table. IBM TDB, Vol. 26, No. 10A, March, 1984, pages 5100-02, describes a mechanical punch with a dense array of punches which is electromechanically affixed to a platen which is driven downward at the appropriate time causing a push rod and punch carrier to be driven down. Simultaneously, a punch is driven down, thereby piercing the substrate material. IBM TDB, Vol. 30, No. 6, November, 1987, pages 355-58, describes a punching apparatus in which a single punch is used to form vias in the substrate by performing punching with the substrate moving at a constant velocity (xe2x80x9con the flyxe2x80x9d). IBM TDB, Vol. 31, No. 9, February, 1989, pages 140-41, discusses a flexpunch machine which uses a punch and die assembly to produce the entire via pattern in the substrate. The punch and die assembly moves at a constant rate while punching the substrate.
Another conventional alternative to a single punch machine is to have an array of equally spaced punches mounted on a bar spanning the width of the substrate being punched and perpendicular to the direction of the movement of the substrate. With this arrangement, the substrate is moved in the direction of the Y-axis and the punches are fired simultaneously as needed. If the spacing of the punches exceeds the grid size of the holes, and if the ratio of grid size to punch spacing is an integer, then the number of passes of the substrate required to complete the punching task is equal to this ratio. For each pass of the substrate, the material is indexed one grid unit along the X-axis and a discrete indexing device for incremental movement of the substrate along the X-axis is required. Further, due to physical size requirements and electric power usage, the simultaneous firing of the punches on the array requires an independent power supply for each punch. The drawbacks of this system include the power supply problems and the requirement that a discrete indexing device, movable in the X direction, be provided.
None of the aforementioned references utilize a punch head having a fixed partial via pattern corresponding to a line of ups which is created from a via fill mask, to perforate a substrate which is supported by a precision die which is also created from the via fill mask having a full array pattern of vias. A problem exists with punching a constantly moving substrate because the punch speed must be extremely high with respect to the substrate speed in order to avoid any distortion such as ripping, tearing, or the like. Conventional systems which punch xe2x80x9con the flyxe2x80x9d must use an extremely large power supply to obtain the necessary punch speed relative to the substrate speed. The need for a large power supply for each punch in an array is impractical because large power supplies have correspondingly large physical size and electric power requirements which limit their use to a single punch or a die set having several plural punches affixed to it.
A conventional system includes cluster punches and cluster dies which are used to punch vias with both being moved together about the surface of the substrate punching a single pattern of holes (ups) multiple times, as required, in the substrate. An illustration of such a prior art system is shown in FIG. 5. In FIG. 5 punch and die assembly 62 is positioned to sandwich greensheet 60. A single pattern is punched in one operation. Also illustrated are positioning system 92, hole verifier 94, and controller 96. The drawback in this system is that the punch and die assembly is subject to alignment errors with respect to the substrate and that, as the number of holes required per ups increases, the precision of the final via pattern decreases. This type of system is typically cost effective only if the total number of vias is less than approximately 3,000.
In another conventional system, the entire hole pattern of a substrate is created in one operation. In this system, a gang punch and die is used to create the via pattern. This system is undesirable because, as the number of vias increases, the cost to create a single large punch becomes prohibitive. Technological demands now require substrates to have greater than 10,000 holes per surface and the cost to create a single punch to provide so many holes becomes unjustifiable in view of consumer demand for lower product cost. Another drawback is that the potential for punch breakage is great and the resulting repair cost is high.
Another conventional system uses a plurality of single punches to produce an entire via hole pattern in a substrate instead of using a gang punch. This system is illustrated in FIG. 6, which shows apparatus 70 which has a plurality of individually activated programmable punching elements 72, supported in punch head 74. Base 76 moves table 78, which supports substrate 80, in the X and Y directions. As substrate 80 is positioned under punching elements 72, computer control unit 82 activates punching elements 72 as required. This system has the disadvantages of requiring complicated programming and the punching operation is time consuming because only one punch is activated at a time.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a linear punch fabricated using mask technology that will have a partial linear pattern of ups for punching a substrate in conjunction with a die which contains a full pattern of ups. It is another object of the present invention to provide a precision punch which has a lower cost to construct. It is yet another object of the present invention to provide a precision punch which aligns with the die before punching the substrate. It is a further object of the present invention to provide a precision punch which will compensate for misregistration of the punch with respect to the die. It is another object of the present invention to provide a precision punch which punches holes of various size. Still another object of the present invention is to provide a precision punch which is less susceptible to breakage.
To solve these aforementioned disadvantages of conventional punch assemblies, and to provide accuracy and repeatability in the creation of vias, the present invention relates to a linear via punch employing a fixed partial pattern of punches to create holes in a substrate by mating with a die which has a full array pattern of holes and is adapted to support a substrate where the substrate is disposed between the punch head and the die so that the punch head punches holes in the substrate and matches corresponding holes in the die.
The present invention also relates to a method for punching and filling vias in a substrate comprising the steps of fabricating a die pattern corresponding to a via fill mask and placing the substrate on the die, positioning the substrate and the die at a position below the punch head, punching vias in the substrate corresponding to a partial pattern of the die, removing the punch from the substrate, and repositioning the punch relative to the substrate to a further position to punch further holes in the substrate.
The present invention further relates to a linear via punch which articulates in at least one of an X position, Y position, and theta position with respect to the die to compensate for die/punch misregistration.
The present invention also relates to a method for punching and filling vias in a substrate comprising the steps of fabricating a die pattern corresponding to a via film mask, placing the substrate on the die, detachably fixing the substrate to the die, positioning the substrate and the die at a position below the punch head, aligning the substrate and the die with the punch head, placing the punch head in contact with the top surface of the substrate, articulating the punch head in at least one of an X position, a Y position, and a theta position with respect to the die, punching at least one via in the substrate corresponding to the die pattern of the die, stepping the substrate and the die to a further position below the punch head, and repeating the punching steps until the die pattern is complete.
The present invention further relates to a linear via punch where the substrate is a greensheet and also relates to a linear via punch where the substrate is a flexible plastic film with a metal coating, such as Kapton(copyright).
The present invention finally relates to a linear via punch for punching holes in a substrate comprising a punch head having a fixed partial pattern, a die having a full array pattern with a portion corresponding to the fixed partial pattern and adapted to support the substrate wherein the substrate is disposed between the punch head and the die such that the punch head is above the substrate and the punch head punches holes in the substrate in a pattern which corresponds to the die array pattern, and alignment means for aligning the punch head with the die, the alignment means having at least one alignment pin on the punch head and at least one locator hole in the die, wherein the punch head articulates in at least one of an X position, Y position, and theta position with respect to the die.